That jumped right out at me too.
Of all the radars in use, ATC, military search bands, civilian weather, and of course other military platforms, why is this only showing in one aircraft type of radar? I know it is newer and more sensitive but anything that shows a doppler shift could paint this.
Another factor is that these anomalies occur over water, not land. One issue that you have already covered, is that the radar is processed and all information displayed is synthetic based on signal processing. I'm not an RF expert but I know that even common systems like AM radio are susceptible to all kinds of noise.
They’ve got visuals. See post #19 above.